As all know, to get to a certain point on the surface of the
ocean, where there is no land to give location, a navigator has
to depend on mathematical calculations. The earth's surface is
divided by imaginary lines. The lines drawn from the north to the
south poles are called meridians of longitude. They are marked in
degrees, and indicate distance east or west of the meridian of,
say, Greenwich, England, which is taken as one of the centers.
The degrees are further divided into minutes and seconds, each
minute being a sixtieth of a degree and each second, naturally,
the sixtieth of a minute.
Now, if a navigator had to depend only on the meridian lines
indicating distance east and west, he might be almost any
distance north or south of where he wanted to go. So the earth is
further divided into sections by other imaginary lines called
parallels of latitude. As all know, these indicate the distance
north or south of the middle line, or the equator. The equator
goes around the earth at the middle, so to speak, running from
east to west, or from west to east, according as it is looked at.
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